The present invention relates to an apparatus and method for controlling the transfer of a fluid from a first container to a second container. Specifically, the present invention relates to a check valve used to control the transfer of fluid from a first container to a second container that has a sub-atmospheric pressure. One application of the present invention is the subdivision of pharmaceutical solutions where a pipetting device is used to transfer a liquid solution into an evacuated container containing a lyophilized drug.
Valve and pump systems for regulating fluid flow are generally known in the art. The prior art shows the use of rotary valves or pinching mechanisms to selectively direct fluid flow. For example, a rotary valve may be manipulated by an air cylinder or other mechanical means to selectively open and close particular fluid flow pathways. Fluid pathways may be pinched-off mechanically by a hinge plate or a cam lobe that presses a fluid containing tube shut to prevent fluid flow. The prior art also teaches the use of pumps and pressure differentials to control fluid flow through a valve system.
In addition, conventional one-way valves are generally known in the art. Conventional one-way valves are configured so a poppet is held against a seat by mechanical means, such as a spring. A conventional one-way valve operates to open only when pressure against the poppet is sufficient to overcome the mechanical means holding the poppet against the seat. The mechanical means of a conventional one-way valve exerts force in a direction opposite the driving force of the pressure gradient across the one-way valve in order to control flow from a high-pressure container into a low-pressure container. The mechanical means in a conventional one-way valve acts against the pressure gradient to keep the poppet in place and prevent uncontrolled flow into the low pressure container. As the pressure gradient between the two containers increases, the mechanical means must exert more and more force against the poppet to keep the poppet seated and the valve sealed.
As the pressure gradient increases, a conventional one-way valve also becomes more prone to "cracking." Cracking occurs when the mechanical means fails to keep the poppet seated because of the large pressure gradient across the one-way valve. When cracking occurs fluid flows through the valve and into the low-pressure container until the pressure difference between the two containers has diminished enough to allow the crack in the valve to reseal. As a result, conventional one-way valves are less reliable when used in applications where precise amounts of fluid must be transferred from a container at ambient pressure to a low-pressure container.